The subject matter of the present invention relates to apparatus for measuring a temperature in a wellbore, and more particularly, to a sidewall contact temperature tool adapted to be disposed in a wellbore including a pad assembly having a pair of sensors, each sensor of the pad assembly including a knife edge for cutting into a mudcake disposed on a wall of the wellbore and contacting an earth formation traversed by the wellbore for measuring a temperature of the formation and not the mudcake.
When a well tool apparatus is disposed in a wellbore, mud normally fills the hole; as a result, the mud accumulates on a wall of the formation traversed by the wellbore thereby forming a mudcake. Various wellbore apparatus of the prior art have measured the temperature of the mud in the wellbore, and other wellbore apparatus have measured the resistivity of the formation traversed by the wellbore. For example, a prior art wellbore apparatus known as the Microlog Resistivity Tool (MLT), available from Schlumberger Technology Corporation, Houston, Tex., measures the resistivity of the formation traversed by the wellbore. The MLT included a tool body, an arms assembly connected to the tool body, and a pad assembly connected to the arm assembly for measuring the resistivity of the formation when the arm assembly, in response to instructions from the tool body, extends the pad assembly into contact with the mudcake which has accumulated on the wall of the formation. The pad assembly of the MLT was smooth on its base, the smooth base of the pad assembly contacting the mudcake (and not the formation) when the resistivity of the formation was measured. In addition, another prior art wellbore apparatus known as the Measure While Perforating Sonde included a probe sensor for measuring the temperature of the fluid in the wellbore, and a separate sensor for measuring the pressure of the fluid in the wellbore. However, none of the aforementioned prior art wellbore apparatus measured the actual temperature of the formation, and not the mudcake, which is traversed by the wellbore.